1. Field of the Invention
The present invention relates to a circuit arrangement for driving the printing jets in mosaic printers, employing tubular drive elements of polarized ceramic, which contain printing liquid and whose diameter reduces with the application of a voltage in the direction of the polarizing voltage and increases with the application of a voltage in opposition to the polarizing voltage.
2. Prior Art
German Offenlegungs-schrifts No. 2,144,892 discloses a pulsed droplet ejector device comprising a tubular piezoelectric component whose internal volume changes in response to electrical signals and in so doing ejects printing liquid contained in the tubular component. This piezoelectric transducer is driven in such a fashion that in the inoperative state it is in an expanded condition, as the result of the application of voltage thereto of a polarity opposite to the original polarizing voltage applied to the piezoceramic. To eject said printing liquid, an electronic switch system, e.g. a switching transistor is provided, by means of which the applied voltage is short-circuited, whereupon the transducer reacts with a sudden contraction and thus ejects a small quantity of liquid. After the ejection of a droplet, the transducer again has the original voltage applied to it and recycles to its expanded condition.
This kind of drive has the drawback that only a relatively small working stroke can be achieved with the piezoceramic because, due to the permanently applied control voltage which is in opposition to the original polarizing voltage, there is the risk of depolarizing the ceramic.
If, when using this kind of drive system, several jets are operated, then a separate voltage source must be provided for each printing jet and it is an expensive procedure to effect switching of voltages of this order.